1. Technical Field
The present invention relates to a composite for forming a ferroelectric thin film used for forming a ferroelectric thin film in accordance with the MOD (metal organic deposition) method, a ferroelectric thin film, a method of manufacturing a ferroelectric thin film, and a liquid-jet head.
2. Related Art
A ferroelectric thin film containing a crystal represented by lead zirconate titanate (PZT) and the like possesses spontaneous polarization, high dielectric constant, an electro-optic effect, a piezoelectric effect, a pyroelectric effect, and the like and is therefore applied to a wide range of device development including piezoelectric elements. Meanwhile, methods such as the MOD method, the sol-gel method, the CVD (chemical vapor deposition) method and the sputtering method are known as the methods of forming such a ferroelectric thin film. In particular, the MOD method and the sol-gel method have an advantage that it is possible to form a ferroelectric thin film easily and at relatively low costs.
When forming the ferroelectric thin film in accordance with the MOD method, the film is typically formed by dissolving an organometallic compound such as a metal alkoxide in an alcohol, coating a colloidal solution obtained by adding a hydrolysis inhibitor or the like thereto on a target object, and drying and sintering the solution on the target object. Meanwhile, when forming the ferroelectric thin film in accordance with the sol-gel method, the film is formed as similar to the MOD method except that the method applies a colloidal solution obtained by dissolving an organometallic compound in an alcohol and subjecting this organometallic compound solution to hydrolysis and a polycondensation reaction while adding the required minimum amount of water thereto (see Patent Document 1, for example).
Here, the methods of manufacturing a ferroelectric thin film applying the MOD method and the sol-gel method will be described in detail. A composite for forming a ferroelectric thin film pooled in a tank is conveyed to a nozzle which is disposed above a target object by use of dry inert gas (carrier gas) such as dry nitrogen gas, and the composite for forming a ferroelectric thin film is dropped from the nozzle onto the rotating target object. In this way, a precursor film is formed on the target object and then turned into gel by drying and degreasing, and a ferroelectric thin film is manufactured by further sintering the film on the target object.
However, in terms of the composite for forming a ferroelectric thin film used for forming the ferroelectric thin film in accordance with the MOD method or the sol-gel method, the alcohol (the solvent) contained in the composite for forming a ferroelectric thin film vaporizes in the dry inert gas environment where the composite contacts the dry inert gas. As a result, there is a problem of deterioration in dispersion stability of the organometallic compound which leads to sol aggregation and deposition. Moreover, when the composite for forming a ferroelectric thin film is pooled in the tank or the like for a certain period, there is also a problem of deterioration in preservation stability of the composite for a ferroelectric thin film (the organometallic compound) attributable to sol deposition.
Here, when the sol is deposited, the sol composition in the composite for a ferroelectric thin film may be altered and a film component in the ferroelectric thin film may be unevenly dispersed, whereby a piezoelectric characteristic of a piezoelectric element including the ferroelectric thin film may fluctuate. In addition, in a liquid-jet head including the piezoelectric element as a piezoelectric actuator, the fluctuation of the piezoelectric characteristic of the piezoelectric element may lead to unevenness in a liquid-jet characteristic.
Patent Document 1: JP-A-6-5946